This invention relates to a process for forming a starting profile or a similar workpiece into an end profile by means of an internal high pressure produced in the sealed profile cavity by way of a fluid active means, in particular for forming until the end profile rests against the wall of a form chamber. In addition, the invention comprises a profile with a profile area separated by at least one profile wall as a starting profile for the performance of the process.
In so-called internal high pressure forming (IHPF process) a hollow profile is elongated by means of internal pressure. In addition, the hollow profile can be pushed by means of at least one pusher on the workpiece and stretched, compressed, or expanded.
DE 35 32 499 C1 discloses for example a device to hydraulically expand a pipe section by using a peg-like cylindrical probe inserted in the pipe, which by means of at least two spaced ring seals creates a seal area with the pipe section to be expanded, which is filled with pressure medium in order to expand the pipe. Before the start of the expanding process, the two ring seals are filled with pressure medium to seal the ring gap between the probe and the pipe. The pressure medium is supplied to the ring area by way of at least one reception slot and is controlled by a ring seal which serves as a valve and which closes the opening found between the reception slot and the ring area until it has achieved its seal effect by way of elastic expansion.
This internal high pressure forming or hydro-forming is increasingly used as an economic manufacturing procedure for bodywork components in car construction. Tubular steel is predominately used as the starting material. Recently, for IHPF processes, aluminium material has also been added to the steel. In the same way as steel, this gives manufacturing procedures in which tubes of sheet aluminium are used as starting material; however, aluminium extrusion profiles may also be used as an alternative. This is out of the question in the case of steel for economic reasons. The use of extrusion profiles has the decisive advantage that there are almost no limits to the shaping of the starting profile.
For forming metallic tubes or extrusion profiles by means of bending, an attempt is generally made to organise the bending process in such a way that the starting cross-section of the workpiece remains contained in the then curved workpiece. Folds on the internal radius and on the outer radius should be avoided. Various techniques have been developed in order to achieve this aim; as an example a few such procedures are listed:
stretch bending;
bending over a mandrel;
hot bending.
Such bending techniques are also applied in the case of curved hydro-forming components, the manufacture of which involves a bending process before internal high pressure forming.
In view of these facts, the object of the present invention is to find an alternative bending procedure for hydro-forming components, thereby deliberately avoiding in the bending forming process the aim of giving or maintaining a shape which most closely resembles the contours of the final cross-section to be formed.
The doctrine of the independent claim leads to solution of this task; the sub-claims indicate favourable further embodiments. In addition the invention includes all combinations of at least two of the characteristics contained in the description, the depiction and/or the claims.
In accordance with this invention, before forming through internal high pressure, the starting profile at a distance from its free ends and across its longitudinal axis is formed into a cross-section with favourable bending properties, notably into a flat or roughly oval cross-section. It has also proved favourable to assign to a tool the starting profile with the area to be distorted, which for example is extruded from a light metal alloy or bent and constructed from a sheet metal, and to distort the cross-section by means of this tool; in addition the starting profile should be bent after the distortion cross-sectionally around this area.
The invention also includes mounting the starting profile on a stationary tool and distorting and bending its cross-section by way of a translatory and rotationally movable counter-tool.
An advantageous starting profile for the procedures in accordance with this invention is an approximately H-shaped cross-section with two roughly parallel chambers connected to each other. Their supporting walls should be cross-sectionally bent inwards, whereas the inner boundaries of the chambers are formed by groove-like recesses.
In this case a combined bending IHPF process is used for which no limits are set regarding the choice of starting material in principle; the latter can for example be aluminium, steel or any other metal, if necessary even a non-metallic material. The following bending procedure methods can be distinguished for use in combination with the IHPF process:
a preceding deformation into a cross-section with favourable bending properties;
an accompanying forming into a bendable cross-section during the bending process;
a shaping of bendable cross-sections in extrusion profiles, preferably from an aluminium alloy, without the preceding or accompanying forming process.
The inventor forces targeted folds during bending or he compresses the material flat; if necessary he shapes extrusion profiles in the starting condition correspondingly as flat upright profiles in order thus to achieve a small moment of surface inertia so that corresponding slight plastic distortions are produced in the bending forming process. Only in the ensuing IHPF process will the workpiece be shaped to its final form.
In the combination of bending and IHPF process in accordance with this invention there is a distinct separation of tasks:
the bending process is used to shape the component centre line,
the IHPF process is used to form the cross-section.
In this procedure above all a minimisation of the degree of forming is achieved rather than a simplification of technical complexity with regard to bending. In the bending process in accordance with this invention, the achieved degree of forming is diminished substantially compared to a bending process after a procedure taken from the state of the art. With a classic bending technology in which the aim of the bending process is to achieve a cross-sectional contour as close as possible to the desired end result, only in exceptional cases are favourable results achieved in relation to the accumulated plastic distortions. In contrast, in the use of the bending strategy in accordance with this invention, due to the lower forming degree in the ensuing IHPF process, a higher residual forming capacity is available.
The bending procedure in accordance with this invention for the manufacture of IHPF components offers substantial advantages, including:
Greater shaping can be achieved in the IHPF process with the same material, i.e. there is more freedom in the shape of the end contour of a IHPF component; and
IHPF components with far smaller radii of curvature are possible with the same cross-sectional dimensions.